27
Figure 21: Temperature contour of vertical cross section from centerline of combustor
with 2 cm thickness insulation (Re = 440, at limit).
Since the inaccuracies occur due to the quasi-1D assumption, the accuracy of 2D
model should be affected by the height of combustors. To study this, 3D and 2D models
with different height (2.85 cm, 5 cm, and 10 cm) but the same turns (3.5 turns) and
channel width (3.5 mm) were built. Figure 22 shows the comparison of extinction limits
between 2D and 3D model of the 3 different height combustors. The predictions of 5 cm
tall combustors are very similar in both 2D and 3D model, while 2.85 cm and 10 cm tall
combustors show not very consistent results between their 2D and 3D predictions,
especially at low Re region. The difference in 2.85 cm tall combustor is expected
because the quasi-1D heat loss model slightly underestimates the out-of-plane heat loss
(Table 1). Therefore, the shorter the combustor is, the larger the difference between 2D
and 3D models. However, this cannot explain why 10 cm tall combustor also showed
larger difference between its 2D and 3D model than that in 5 cm tall case.

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27
Figure 21: Temperature contour of vertical cross section from centerline of combustor
with 2 cm thickness insulation (Re = 440, at limit).
Since the inaccuracies occur due to the quasi-1D assumption, the accuracy of 2D
model should be affected by the height of combustors. To study this, 3D and 2D models
with different height (2.85 cm, 5 cm, and 10 cm) but the same turns (3.5 turns) and
channel width (3.5 mm) were built. Figure 22 shows the comparison of extinction limits
between 2D and 3D model of the 3 different height combustors. The predictions of 5 cm
tall combustors are very similar in both 2D and 3D model, while 2.85 cm and 10 cm tall
combustors show not very consistent results between their 2D and 3D predictions,
especially at low Re region. The difference in 2.85 cm tall combustor is expected
because the quasi-1D heat loss model slightly underestimates the out-of-plane heat loss
(Table 1). Therefore, the shorter the combustor is, the larger the difference between 2D
and 3D models. However, this cannot explain why 10 cm tall combustor also showed
larger difference between its 2D and 3D model than that in 5 cm tall case.